The Hybrid – BioVGE project is proposed with the primary objective to develop, design and demonstrate a highly integrated solar/biomass hybrid air conditioning system for space cooling and heating of residential and commercial buildings that is affordable, operating with improved efficiency and with a strong market potential. The developed system will contribute to the improvement of existing technologies from several aspects, including cheaper collector design; targeted thermal energy storage system; compactness; integrated controller for automated and efficient operation; improved reliability and performance; improved monitoring of energy usage; improved scalability. The proposed system will be driven by heat, using two renewable energy resources: solar thermal and biomass. Only a small amount of electricity will be needed for the circulation pumps and the control system (less than 5% of the total needs), thus it is expected that 95% of the building thermal load will be satisfied by renewable energy. It is also expected that the solar fraction for heating will be at least 40% (Central European climate).
Major components of the proposed system are the solar collector field, biomass boiler, thermal energy storage unit using PCM, thermally driven variable geometry ejector (VGE) chiller, heat distribution and intelligent integrated control system. Solar energy will be the primary source of energy when radiation is available. Biomass will act as an auxiliary energy source during cloudy days and night hours. During the cooling season, a VGE chiller will produce cold water using heat from the storage unit or directly heat from the collectors. The chiller will operate with generator temperatures between 75 – 95ºC, and the chilled water temperature will vary in the range of 5 – 15ºC. The variable geometry ejector design will allow the chiller to operate with optimal efficiency under variable operating conditions that is expected using the solar heat source so that biomass consumption can be minimised. It is expected that average thermal and electrical COP of the chiller will be >0.4 (about 0.5) and >5, respectively, approximately 50% better than the performance of fixed geometry cycles on the seasonal basis. During the heating season, heat will be directly transferred from the thermal energy storage unit to the indoor space using the same heat/cold distribution equipment. In heating mode, the temperature of thermal energy storage unit will be lower than in cooling mode, up to 65ºC. Another objective is to design the Hybrid – BioVGE system so that it can also be easily integrated e.g. with domestic hot water (DHW) production and pool heating. DHW can be produced using solar energy during low heating and cooling load periods, while swimming pool heating can be carried out using the heat dissipated by the condenser of the VGE cycle. This way the overall energy efficiency of the proposed system can be further improved.
It is an objective of the work to optimise component design for the Hybrid – BioVGE system. Solar thermal collectors and biomass boilers are mature technologies when they are used as individual heating systems, however their integration into a compact unit still requires innovation effort. Thermal energy storage for solar heat is a common practice, but there is still a debate about its application with biomass boilers. Therefore, there is a need to optimise storage capacity and heat exchanger design and storage medium for the hybrid space heating/cooling system. Variable geometry ejector cooling using solar energy has been demonstrated by INEGI to boost ejector performance under variable operating conditions. There is a need for the optimisation of the control strategy and working fluid selection for residential and commercial buildings. Optimised system design requires a suitable computer tool. Thus yet another objective of the work is to develop a unified design software that will assist component selection and forecasts of the expected performance of the Hybrid – BioVGE system.
An important objective of the proposed work is to develop an intelligent energy monitoring and control unit. The system control will lead to the efficient operation of its components with reduced operating cost and little need for interference by the end user. Real-time monitoring will allow the user and the general public to follow real-time energy performance data that are easy to interpret. This will also contribute to a faster market pick up for the Hybrid – BioVGE system.
Finally, a fundamental objective of the proposed project is to construct and test the performance of three Hybrid – BioVGE systems, adequate for residential and small commercial buildings, under different European climate conditions: heating load dominated; balanced heating and cooling load; and cooling load dominated. Two of the prototypes will have approximately 5 kW/15 kW cooling/heating capacities, adequate for single family homes. The 3rd unit will be designed for 20 kW/50 kW cooling/heating capacity range, suitable for a small commercial or office building. One of the smaller units will be tested under relevant operating conditions using the “Concise Cycle Test” (CCT). The other two units will be installed in real buildings for operating environment testing. The results from the demonstration activity will provide open access scientific data to the broad public while moving up the TRL scale to 7 of this innovative solar/biomass hybrid space heating and cooling solution.